Heretofore, radioactive solutions of iodine 131 have been employed in a wellbore, followed by an overflush of a non-radioactive liquid to get the radioactive liquid out of the wellbore before nuclear logging. Thereafter, a nuclear log survey was run to determine where the liquid went when it left the wellbore and entered the surrounding formation. A problem with liquid radioactive tracer surveys has been that if the overflush is too large, the radioactive liquid can be washed so far away from the wellbore that the nuclear log survey cannot detect the liquid since it has been flushed beyond the range of the logging tool.
Also, heretofore, propping agents used in fracturing treatments have been radioactively tagged to determine where the propping agent went. The propping agents used are normally large, i.e., greater than 40 mesh (U.S. Sieve Series) in order to prop the fracture open as far as possible.